Racket-stringing machine with automatic locking

ABSTRACT

A turntable having an upright U-shaped yoke, provided with clamps for holding a horizontally disposed racket frame at its top, is automatically locked during successive power-actuated pulls of the string in stringing. The string is pulled by a hydraulic cylinder to accurate tension determined by the hydraulic pressure for which there is an adjustable relief valve and gauge. The piston of the cylinder operates a pull bar along which the pulling clamp may be shifted laterally so as to pull in the most advantageous direction. The cylinder is slightly shiftable. The return stroke of the pull bar is limited before the piston seats. Reaction to the retracting pressure releases a spring-set brake to make the yoke free to turn; and reaction to the pulling pressure reinforces the braking force of the spring. A holding clamp can be manually shifted to an advantageous position within the frame when fully released, and the manual closing stroke on its operating lever first raises it to string height, then completes the clamp closing operation and locks the clamp to the turntable, so that it swings with the racket between successive pulls. The parts are so positioned and dimensioned that a racket frame may be strung in both directions without releasing it from the swingable yoke.

United States Patent Krueger et al.

[4 1 Jan. 18, 1972 154] RACKET-STRINGING MACHINE WITH AUTOMATIC LOCKING [72] Inventors: Harvey R. Krueger, Carpentersville; Dean R. Armentrout, Park Ridge, both of I11. [73] Assignee: Court and Slope, Inc. [22] Filed: May 31, 1968 [21] Appl. No.: 733,601

[52] US. Cl. ..73/145, 273/73 A [51] Int. Cl ...GOI15/00, G011 7/00 [58] Field of Search ....273/73 1, 73 A; 73/145 FOREIGN PATENTS OR APPLICATIONS 429,526 5/1935 Great Britain ..273/73 Primary Examiner-Richard C. Pinkham Assistant Examiner- Richard J. Apley Attorney-Darbo, Robertson & Vandenburgh 5 7] ABSTRACT A turntable having an upright U-shaped yoke, provided with clamps for holding a horizontally disposed racket frame at its top, is automatically locked during successive power-actuated pulls of the string in stringing. The string is pulled by a hydraulic cylinder to accurate tension determined by the hydraulic pressure for which there is an adjustable relief valve and gauge. The piston of the cylinder operates a pull bar along which the pulling clamp may be shifted laterally so as to pull in the most advantageous direction. The cylinder is slightly shiftable. The return stroke of the pull bar is limited before the piston seats. Reaction to the retracting pressure releases a spring-set brake to make the yoke free to turn; and reaction to the pulling pressure reinforces the braking force of the spring. A holding clamp can be manually shifted to an advantageous position within the frame when fully released, and the manual closing stroke on its operating lever first raises it to string height, then completes the clamp closing operation and locks the clamp to the turntable, so that it swings with the racket between successive pulls. The parts are so positioned and dimensioned that a racket frame may be strung in both directions without releasing it from the swingable yoke.

19 Claims, 10 Drawing Figures mimmmwm 3535 080 SHEET 2 BF 5 .ZA I g9 64 IIHH' Inve nkors Harveg R .Krueger Dean R. Armen't rout PATENTEB JAN 1 8 I972 SHEET 5 OF 5 rt 13% rev W out trn e K vm WE mwnmmw R in if i D 2 RACKET-STRINGING MACHINE WITH AUTOMATIC LOCKING INTRODUCTION The invention of which this disclosure is offered for public dissemination in the event adequate patent protection is available relates to machines for aiding in the stringing of tennis rackets and the like.

Although machines for the purpose stated have been known for many years, they have been far from fully satisfactory. A racket could be strung by a skilled worker entirely by hand more quickly than with the use of a machine and with more uniform tension on the strings. Furthermore, the energy for pulling the strings usually was derived from the worker, not from the machine.

According to the present invention, several features contribute to more uniform tensioning and to faster operation, and the energy for pulling the strings is all supplied by power. The combination of a laterally shiftable pull clamp and automatic locking of the turn yoke to which the racket is clamped permits pulling the string at the most advantageous angle so that friction will have minimum effect in disturbing the equality of successive pulls. The pulling is performed by hydraulic power by pressure accurately adjusted and readable on a gauge. The pull cylinder also controls a locking brake so that the turntable is locked as the pull begins. The braking or locking force is automatically increased by the reaction to the pull. Springs also contribute to the braking or locking force, the pressure applied by these springs being overcome by the return stroke of the cylinder and piston combination which performs the pull. The holding clamp automatically drops.

below the string level when released and is then freely movable to the proper position for its next task at which time actuation of the clamp lever or handle both raises it into position and locks it to the turntable.

Additional objects and advantages of the invention will be apparent from the following description and from the drawings.

DESIGNATION OF FIGURES FIG. 1 is a perspective view of the machine chosen for illustration of this invention with a cover removed, and shown in the course of stringing a racket;

FIG. 2 is a view looking down on the machine of FIG. I with the cover and racket clamping jaws removed;

FIG. 2A is a similar view on a larger scale, with some parts removed or in section, cylinder 18 being retracted;

FIG. 3 is a fragmentary sectional view taken mainly along the line 3-3 ofFIG. 2A;

FIGS. 4 and 5 are respectively side and top views of the racket holder and the lockable mounting for the holding clamp, with some parts broken away to a sectional view;

FIGS. 6, 7 and 8 are views from two sides and the top of the holding clamp, with supporting parts shown in FIG. 6;

FIG. 9 is a diagram, mainly hydraulic but with some electric control. 0

GENERAL DESCRIPTION As seen in FIG. 1, the machine chosen for illustration includes a base 11, a turntable 12 rotatably carried by the base 11 and formed mainly of a yoke 13 at the top of which the racket 14 to be strung is clamped. The string to be pulled for tensioning is placed in clamp 16, which is closed by manual operation of its handle 82. A button 17 is then pressed, whereupon fluid is supplied to hydraulic cylinder 18 to the rear of the piston therein pushing pull bar 19 outwardly toward the operator. Since clamp 16 is carried by this pull bar, this pulls the string, applying an exact tensioning to it which may be read on gauge 21, on front panel 20, having been set by relief valve control knob 22. While this tension is held on the string, holding clamp 23, having been released from its previous holding task, is moved to a position under the freshly pulled string, just inside of the frame near the pull clamp 16.

Closing the handle of clamp 23 first raises it to a position to seize the string, then closes upon the string and simultaneously locks the clamp base 68 to the turntable I2. Clamp 16 is now manually opened, and by button 17 the pressure fluid is supplied to the other end of cylinder 18, thereby returning pull rod 19 and releasing the brake previously holding turntable 12. The turntable 12 is now swung approximately by hand, clamp 23 moving with it so as to hold the tension of the string. The free end of the string is now threaded through the next aperture and slipped between the jaws of clamp 16 whereupon the operating cycle previously described is begun again.

DETAILED DESCRIPTION OF BEST FORM CONTEMPLATED TURNTABLE STRUCTURE The mounting of the turntable is best seen in FIG. 3. A spool 26 is rotatably mounted around the upper stub end of a fixed shaft 27. A horizontal channel bar 28 is secured to the spool 26, and carries the yokes 13, the upper ends 29 of which form the fixed jaws for supporting and clamping the racket being strung. A threaded stud 31 extends upwardly from each jaw -29, and a movable jaw 32, moved by a nut 33 which may be a wingnut completes the clamp in each instance. The yokes 13 are adjustable along channel bar 28 to fit different rackets, being secured in any adjusted positions by screws 34. Channel bar 28 has extending through it and welded to it a threaded stud 36, the head 37 of which pilots into spool 26 thereby centering the stud 36 and the channel bar 28, and perhaps positioning threaded stud 36 more rigidly. Screws secure channel bar 28 to spool 26.

A deeply slotted spool 38 is threaded on stud 36 and locked in place with a locknut 39. By loosening the locknut, spool 38 may be adjusted in height to adjust the height of the holding clamp 23 carried by it.

It is thus seen that the entire turntable 12 is free to rotate on shaft 27, except when locked by brake bar 41.

COMBINED BRAKING AND PULLING The pulling of the string and the braking of the turntable are both accomplished by hydraulic cylinder 18. As seen best in FIG. 2, the cylinder 18 (with its hexagonal heads 43 and 44) is nested between the upstanding flanges 46 of the two channelshaped brackets 47. The heads 43 and 44 are not secured to the channel brackets and therefore cylinder 18 is free to move longitudinally, and can accommodate itself vertically to the positioning determined by its working connections.

When pressure fluid is supplied to rear head 44, it tends to press piston 48 and piston rod 49 outwardly. The hydraulic pressure likewise bears on rear head 44 tending to press it and cylinder 18 rearwardly. Rear head 44 is formed with a stud 51 which is secured firmly to brake bar 41 as by being threaded into it. Brake bar 41 is also pressed rearwardly by sliding actuator rods 52, which fit it loosely and are biased by springs 53. Thus, when the fluid supply to cylinder 18 permits, springs 53 press the sliding actuator rods 52, which in turn press brake bar 41 into engagement with spool 26. The brake bar has beveled faces 56, and as seen in FIG. 3, spool 26 has correspondingly beveled faces 57 forming the sides of a peripheral groove in it. Thus, brake bar 41 engages the spool with a wedging action which firmly locks it. A 3 bevel is suitable.

Continued hydraulic flow to head 44 moves pull bar 19 outwardly or forwardly, thereby moving pull clamp 16 likewise, to pull the string to which the pull clamp 16 will have been manually clamped. As the string resists the pull, the hydraulic pressure within cylinder 18 will build up to the maximum for which pull regulator 22 has been set and this same maximum hydraulic pressure will press the cylinder 18 rearwardly to increase the pressure of brake bar 41 on spool 26, thereby making certain that the pulling tension does not cause turning of the turntable.

Before clamping the string in the pull clamp 16, the pull clamp may be slid along bar 19 to a desired location and the turntable manually turned at the same time to provide pulling at the most desirable angle with respect to the frame of the racket, thus minimizing variations in tensioning of the strings due to varied frictional conditions.

It is important that the pull bar 19 be guided in a manner to minimize friction resulting from the fact that the tension of the string tends to lock the sliding structure. Any reliable form of parallel movement device could be used but that which has been found to be satisfactory under the varied and compound cantilever forces here present is that which is illustrated. Pull guide bars 61 are firmly secured (as by threads) to cross head 62 on which the pull bar 19 is mounted. Each of the pull guide bars 61 slides smoothly in a bearing cylinder 63 extending through flanges 46 and secured therein by snaprings 64. Bearing cylinder 63 is fitted at each end with bearing sleeves 66 with which the guide rod 61 is smoothly guided. Friction must be very nearly uniform with all positions of pull clamp 16. This is difficult to achieve but is achieved using a Thompson linear ball bushing for each of the bearing sleeves 66.

When hydraulic fluid is supplied under pressure through front head 43 of cylinder 18, piston rod 49 and cross head 62 are moved inwardly (rearwardly) until cross head 62 strikes guide cylinders 63. At this time, the pressure within cylinder 18 builds up to the maximum (which may be higher than that permitted by regulator 22). This hydraulic pressure urges cylinder 18 outwardly in the direction to withdraw brake bar 41 from spool 26, and hydraulic pressure available should be high enough to do so, overcoming the force of springs 53. The turntable is thus again free to be turned, and it is turned by hand approximately 180 preparatory to pulling the next run of string in the opposite direction.

COMBINED ACTION OF HOLDING CLAMPS While a string is being held under tension by the pull clamp 16, holding clamp 23 will be manually released from the point on the former run of string to which it has been secured, swung about 180 and reapplied to the new run of string to hold it tensioned while the pull clamp is released and the turntable swung 180 preparatory to pulling the next run of string. During the i80 swing of the turntable, the holding clamp must be locked to the turntable.

As seen in FIG. 6, the holding clamp 23 is a self-locking toggle-type clamp, carried by a shiftable but lockable base 68. This base 68 is provided with an upstanding socket 69. A clamp body 71 is provided with a shank sleeve 72 snugly fitting the socket 69 to be turnable and vertically shiftable therein. The upward shifting movement is limited by a snapring 73, fitting in a groove in shank 72. The upper end of the clamp body 71 is supplied with a fixed jaw 74. A movable jaw 76 cooperating with jaw 74 is pivoted to the body 71 by a pin 77, held in place by snap ring 78. A compression spring 79, positioned in a suitable socket, may be provided for urging the jaws to the opened position. The jaws are preferably provided with friction face plates 81.

A clamp handle 82 is floatingly associated with body 71 by means of an actuator pin 83 and a toggle link 84. The actuator pin 83 presses movable jaw 76 upwardly when handle 82 is actuated toward body 71, or inwardly. If for convenience pin 83 projects beyond the fin 86 by which it is carried, it may move idly in a recess provided for it in body 71.

Toggle link 84 is pivoted to the lower portion of fin 86 on handle 82 and to the upper end of thrust rod 87. Thrust rod 87 bears on adjustment screw 88 by which it has adjustable coaction with locking lever 89.

As handle 82 is swung downwardly, it combines with toggle link 84 to form a double toggle linkage which, as it begins to straighten out, raises clamp body 71, thereby raising the jaws 74 and 76 to lie on opposite sides of the string about to be clamped. Inasmuch as the clamp body 71 and handle 82 will be jointly grasped in one hand, this quickly becomes an automatic positioning action. Continued downward and inward movement of handle 82 further straightens out the toggle linkage but since upward movement of body 71 is now limited by snapring 73, the toggle linkage exerts upward pressure on movable jaw 76 and downward pressure on locking lever 89. The upward pressure firmly clamps the string which is under tension due to the pull thereon by pulling clamp 16. The locking lever 89 firmly locks the holding clamp 23 against any relative movement between it and the turntable. Thus, when the turntable is free to turn, it, the clamped racket, and clamp 23 holding the tensioned string will all move as a unit.

As seen in FIG. 4, the clamping lever 89 is pivoted by a pin 91 to shiftable clamp base 68, both being bifurcated to lie within the deep groove of spool 38, but to be shiftable a substantial distance therein. This distance is limited by the depth of the slot 92 in one direction and by pin 91 in the opposite direction to the extent of movement at which locking will take place. When locking lever 89 is pressed downwardly by thrust pin 87, locking lugs 93 are pressed onto the lower flange of spool 38, while a substantially equal pressure is exerted against the upper flange by shiftable base 68. Thus, the holding clamp assembly is firmly locked to spool 38 which in turn is firmly locked to the turntable structure. Adjustment screw 88 simultaneously adjusts the pressure of jaws 74, 76 on the string and the locking pressure at lugs 93.

PULL CLAMP The pull clamp 16 may be essentially like the holding clamp 23. However, the adjustment screw 88A will be threaded into the bottom of shank sleeve 72A of body 71A, which is free to turn in socket 69A, but not to move up and down. Socket 69A is part of slide bracket 94, slidable on pull bar 19. As seen in FIG. 3, slide bracket 94 is normally in the vertical position, resting on crosshead 62. It can swing downwardly to the dotted line position to let the racket handle swing past clamp 16.

HYDRAULIC AND ELECTRICAL CIRCUITS The hydraulic and electrical circuits are sufficiently indicated in FIG. 9. The parts not already described include a pump and reservoir so designated in the drawing and a relief valve 96 which determines the maximum pressure to be delivered by the pump. The pump is preferably a positive displacement pump. It is driven by an electric motor, not shown, controlled by a main switch. A needle valve 97 controls the speed of hydraulic flow and hence the speed of operation of the parts. A two-position, four-port hydraulic valve 98 is controlled by a solenoid 99 which in turn is controlled by button 17. The valve 98 is biased, as by a spring, to the position connecting the source of hydraulic fluid to head 43 and connecting head 44 directly to the reservoir. When the circuit controlled by button 17 is closed, solenoid 99 actuates valve 98 to its other position, connecting the source of fluid under pressure to head 44 and head 43 directly to reservoir. In this instance, the adjustable relief valve 22 limits the pressure applied through head 44 to the adjusted value, the pressure at any instant being shown on gauge 21. The switch represented by button 17 is preferably closed and opened on successive pressings of the button or it can be foot-actuated if desired, leaving both hands free.

A second gauge 101 is preferably provided so that the operator can be sure the pump is operating effectively and roviding sufficient pressure to overcome springs 53, as well as to provide a safe excess over the setting of pull pressure controller 22. If relief valve 96 is adjustable, gauge 101 may also be used as a guide in the adjustment.

OPERATION The operation is apparent for the most part from the description under the heading "General Description."

As those familiar with racket stringing will know, the first step of a racket stringing operation after clamping the racket frame to the turntable, is to anchor the portion of the string from which the string is to be drawn in tensioning it. Usually this will be a midpoint of a string, anchoring it at a midpoint of the frame. For this purpose, any suitable starting peg or clamp can be used, and it has no connection with the machinery. At present, a small screw-actuated clamp is preferred, but it is not illustrated, in view of the independence of the invention from the details of this clamp. After the stringing of one string in one direction from the starting clamp has been completed, by successive pulls of the pull clamp 16 and holding the string by holding clamp 23 between successive pulls, and when the string has been permanently secured at that end, the stringing will proceed from the holding clamp toward the other end of the string. When the first run in this direction is pulled to the desired tension by the pull clamp 16, the starting clamp will be removed, and the holding clamp 23 will be applied to hold the tension until the next run has been pulled to the desired tension by the pull clamp.

ACHIEVEMENT It is apparent from the foregoing that all of the pulling of the strings is done by power, instead of by energy supplied directly or indirectly by the stringer. Great uniformity of tensioning can be achieved, partly because the tensioning force is determined by accurately adjusted hydraulic pressure, and partly because during each pull the racket can be turned and held at such an angle, and the clamp moved laterally to a suitable position, so that the pull is in the direction least affected by friction. The automatic locking of the turntable during pull avoids any wasted time at this point. It is important not to waste even seconds in an operation which must be repeated many times during the stringing of a racket. The shifting of the holding clamp between successive runs is also achieved at minimum operational time by virtue of the fact that the opening operation of the clamp also releases and lowers it for freedom of movement, and the closing of the clamp lever raises the jaws into the plane of the strings, closes them on the string being held by the pull clamp, and locks the clamp against relative movement with respect to the turntable, again without loss of precious seconds,

The net result is that the quality of the stringing operation, with little practice, is comparable to or better than that of skilled racket stringers, stringing by hand, and considerably better than that achieved with the aid of previous machines. An operator quickly develops speed which is comparable to that of a skilled stringer, stringing by hand, and again substantially faster than that achieved by prior machines.

The locking of the turntable and the ability to shift the pull clamp for a chosen line of pull also makes the machine satisfactory for some rackets for which prior machines could not be used, for example, where the wrong angle of pull would shift a string from a notch or recess in which it is intended to rest. These also contribute to the ability to string the racket completely (both cross strings and longitudinal strings) without removal from the turntable.

We claim:

1, A machine for stringing rackets including a base, a turntable rotatably mounted on the base, means for clamping a racket frame to the turntable, a string-holding clamp carried by the turntable and movable into the plane of the strings for holding a tensioned run of string and movable with respect to the turntable at will, a pull clamp having jaws substantially in the plane of the racket and mounted on a movable unit for movement in one direction for pull of a string, a cylinder and piston combination for moving said pull clamp and said unit in the pull direction the pull clamp being mounted for ready and frequent preliminary shifting laterally with respect to the direction of movement of said unit.

2. A machine for stringing rackets according to claim 1 including means for locking the turntable against rotation, means for guiding the movement of the pull clamp while maintaining its movement substantially free from frictional variations resulting from laterally differing positions of the clamp, hydraulic means for actuating the cylinder-piston combinations, and an operator-adjustable relief valve for determining the pulling tension by limiting the pressure delivered to the cylinder during pulling.

3. A machine for stringing rackets according to claim I including means for locking the turntable against rotation.

4. A machine for stringing rackets according to claim 1 including means for guiding the movement of the pull clamp while maintaining its movement substantially free from frictional variations resulting from laterally differing positions of the clamp.

5. A machine for stringing rackets according to claim 1 including automatic means for locking the turntable during the pulling operation.

6. A machine for stringing rackets including a base, a turntable rotatably mounted on the base, means for clamping a racket frame to the turntable, a string-holding clamp carried by the turntable and movable into the plane of the strings for holding a tensioned run of string and movable with respect to the turntable at will, a pull clamp having jaws substantially in the plane of the racket and mounted on a movable unit in one direction for pull of a string, a cylinder and piston combination for moving said pull clamp and said unit in the pull and return directions, and power driven means for supplying fluid to the cylinder, and

automatic means for locking the turntable during the pulling operation; said means being controlled by said cylinder and piston combination.

7. A machine for stringing rackets according to claim 6; said means for locking including a brake normally biased to lock the turntable and released by the cylinder and piston combination at the end of the return stroke thereof.

8. A machine for stringing rackets according to claim 6; said means for locking including a brake normally biased to lock the turntable, and coupled to the reactive portion of the cylinder and piston combination to be urged thereby in the locking direction in reaction to the pulling force, and in the release direction in reaction to a limitation of the return stroke.

9. In a machine for stringing rackets, having a racket holder for holding a racket in a given plane, a tension-holding assembly including a clamp support movable with respect to the racket holder in directions parallel to said plane, a clamp reciprocable on the support perpendicularly to said plane and including jaws movable into said plane to grip a strung string and means directly associated with the clamp, and operable by continuing and unitary movement of the same hand which moved the jaws into said plane, for closing the jaws to grip a string, and for locking the support to hold the clamp and its gripped string.

10. In a machine for stringing rackets having a racket holder for holding a racket in a given plane, a tension-holding assembly according to claim 9; said string-holding clamp being movable to all string-holding positions within the frame and said clamp being pivotable with respect to its support generally about an axis perpendicular to said plane for clamping alignment with strings strung in either direction.

11. In a machine for stringing rackets having a racket holder for holding a racket in a given plane, a tension-holding assembly according to claim 9 in which the means for closing the jaws includes a handle which also operates the means for locking the support.

12. In a machine for stringing rackets having a racket holder for holding a racket in a given plane, a tension-holding assembly according to claim 9 in which the means for closing the jaws includes a handle which in addition produces a reciprocation movement to move the jaws into said plane before the closing movement of the jaws.

13. In a machine for stringing rackets having a racket holder for holding a racket in a given plane, a tension-holding assembly according to claim 9 in which said means for closing causes a reciprocation movement by reaction to its jaw closing effort and said jaws being biased to the open position with sufficient strength to resist closing until the reciprocation movement reaches its limit.

14. In a machine for stringing rackets having a racket holder for holding a racket in a given plane, a tension-holding assembly according to claim 9 in which the racket holder is on a turntable and the means for locking the support locks it to the turntable.

15. In a machine for stringing rackets having a turntable, a racket holder thereon for holding a racket in a given plane,

a tension-holding assembly including a clamp support movable with respect to the racket holder in directions parallel to said plane, a clamp carried by the support and movable perpendicularly to said plane and including jaws thereby jointly movable generally into said plane and closable to grip a strung string, means for closing the jaws to grip a string, characterized by:

means for locking the support to the turntable; said turntable including a spool having its axis near the center of the racket, fixed to the turntable and having a deep annular groove therein; and said clamp support and means for locking both being bifurcated and straddling the axis and being jointly effective to lock the clamp support means by force-spreading against the walls forming the groove.

16. In a machine for stringing rackets having a turntable, a

racket holder thereon for holding a racket in a given plane,

a tension-holding assembly including a clamp support movable with respect to the racket holder in directions parallel to said plane, a clamp carried by the support and movable perpendicularly to said plane and including jaws thereby jointly movable generally into said plane and closable to grip a strung string, means for closing the jaws to grip a string, characterized by:

means for locking the support to the turntable; said turntable including a spool having its axis near the center of the racket, fixed to the turntable and having a deep annular groove therein; and said clamp support and means for locking both being bifurcated and straddling the axis and being jointly effective to lock the clamp support means by force-spreading against the walls forming the groove;

the means for closing the jaw being arranged to perform the force-spreading by reaction to the closing effort.

17. In a machine for stringing rackets having a turntable, a

racket holder thereon for holding a racket in a given plane,

a tension-holding assembly including a clamp support movable with respect to the racket holder in directions parallel to said plane, a clamp carried by the support and movable perpendicularly to said plane and including jaws thereby jointly movable generally into said plane and closable to grip a string, characterized by:

means for locking the support to the turntable; and

string-tensioning means including a pull clamp, means for moving the pull clamp along a line selected at will from a variety of parallel lines displaced laterally with respect to the general direction of pull, and with selected force, and means for locking the turntable during the pull.

18. In a machine for stringing rackets having a turntable, a

racket holder thereon for holding a racket in a given plane,

a tension-holding assembly including a clamp support movable with respect to the racket holder in directions parallel to said plane, a clamp carried by the support and movable perpendicularly to said plane and including jaws thereby jointly movable generally into said plane and closable to grip a strung string, means for closing the jaws to gri a string, characterized by: means or locking the support to the turntable; said turntable including a spool having its axis near the center of the racket, fixed to the turntable and having a deep annular groove therein; and said clamp support and means for locking both being bifurcated and straddling the axis and pivotally associated to each other to lock the clamp support by pivotal action causing locking engagement within the groove;

said clamp having a toggle linkage which upon being straightened thrusts in one direction to cause pivoting of the levers and in the opposite direction for closing the clamp.

19. In a machine for stringing rackets, having a racket holder for holding a racket in a given plane, a tension-holding assembly including clamp support means movable with respect to the racket holder in crossing directions parallel to said plane, a clamp movable with the support means and includingjaws further movable to grip a strung string, means for closing the jaws to grip a string, and means for locking the support means against all movement along said plane to hold the gripped string, said clamp being pivotal as to its support means about an axis generally perpendicular to said plane for alignment of its jaws with a string strung in either of the crossing directions for gripping said string;

said clamp being a toggle clamp in which the jaw closing toggle exerts a thrust perpendicular to the plane to thrust the jaws into adjacency to the strings before gripping the strings and to actuate the means for locking the support,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,635, 080 Dated Jan. 18, 1972 Invent0r(s) Harvey R. Krueger and Dean R. Armentrout It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7, line 10, after "closing" insert includes a handle which 1 Signed and sealed this 29th day of August 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR, 7 ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PC4050 (10459) USCOMM-DC 60376-F 69 (T U45. GOVERNMENT PRINTING OFFICE: I969 0"366'134 

1. A machine for stringing rackets including a base, a turntable rotatably mounted on the base, means for clamping a racket frame to the turntable, a string-holding clamp carried by the turntable and movable into the plane of the strings for holding a tensioned run of string and movable with respect to the turntable at will, a pull clamp having jaws substantially in the plane of the racket and mounted on a movable unit for movement in one direction for pull of a string, a cylinder and piston combination for moving said pull clamp and said unit in the pull direction the pull clamp being mounted for ready and frequent preliminary shifting laterally with respect to the direction of movement of said unit.
 2. A machine for stringing rackets according to claim 1 including means for locking the turntable against rotation, means for guiding the movement of the pull clamp while maintaining its movement substantially free from frictional variations resulting from laterally differing positions of the clamp, hydraulic means for actuating the cylinder-piston combinations, and an operator-adjustable relief valve for determining the pulling tension by limiting the pressure delivered to the cylinder during pulling.
 3. A machine for stringing rackets according to claim 1 including means for locking the turntable against rotation.
 4. A machine for stringing rackets according to claim 1 including means for guiding the movement of the pull clamp while maintaining its movement substantially free from frictional variations resulting from laterally differing positions of the clamp.
 5. A machine for stringing rackets according to claim 1 including automatic means for locking the turntable during the pulling operation.
 6. A machine for stringing rackets including a base, a turntable rotatably mounted on the base, means for clamping a racket frame to the turntable, a string-holding clamp carried by the turntable and movable into the plane of the strings for holding a tensioned run of string and movable with respect to the turntable at will, a pull clamp having jaws substantially in the plane of the racket and mounted on a movable unit in one direction for pull of a string, a cylinder and piston comBination for moving said pull clamp and said unit in the pull and return directions, and power driven means for supplying fluid to the cylinder, and automatic means for locking the turntable during the pulling operation; said means being controlled by said cylinder and piston combination.
 7. A machine for stringing rackets according to claim 6; said means for locking including a brake normally biased to lock the turntable and released by the cylinder and piston combination at the end of the return stroke thereof.
 8. A machine for stringing rackets according to claim 6; said means for locking including a brake normally biased to lock the turntable, and coupled to the reactive portion of the cylinder and piston combination to be urged thereby in the locking direction in reaction to the pulling force, and in the release direction in reaction to a limitation of the return stroke.
 9. In a machine for stringing rackets, having a racket holder for holding a racket in a given plane, a tension-holding assembly including a clamp support movable with respect to the racket holder in directions parallel to said plane, a clamp reciprocable on the support perpendicularly to said plane and including jaws movable into said plane to grip a strung string and means directly associated with the clamp, and operable by continuing and unitary movement of the same hand which moved the jaws into said plane, for closing the jaws to grip a string, and for locking the support to hold the clamp and its gripped string.
 10. In a machine for stringing rackets having a racket holder for holding a racket in a given plane, a tension-holding assembly according to claim 9; said string-holding clamp being movable to all string-holding positions within the frame and said clamp being pivotable with respect to its support generally about an axis perpendicular to said plane for clamping alignment with strings strung in either direction.
 11. In a machine for stringing rackets having a racket holder for holding a racket in a given plane, a tension-holding assembly according to claim 9 in which the means for closing the jaws includes a handle which also operates the means for locking the support.
 12. In a machine for stringing rackets having a racket holder for holding a racket in a given plane, a tension-holding assembly according to claim 9 in which the means for closing the jaws includes a handle which in addition produces a reciprocation movement to move the jaws into said plane before the closing movement of the jaws.
 13. In a machine for stringing rackets having a racket holder for holding a racket in a given plane, a tension-holding assembly according to claim 9 in which said means for closing causes a reciprocation movement by reaction to its jaw closing effort and said jaws being biased to the open position with sufficient strength to resist closing until the reciprocation movement reaches its limit.
 14. In a machine for stringing rackets having a racket holder for holding a racket in a given plane, a tension-holding assembly according to claim 9 in which the racket holder is on a turntable and the means for locking the support locks it to the turntable.
 15. In a machine for stringing rackets having a turntable, a racket holder thereon for holding a racket in a given plane, a tension-holding assembly including a clamp support movable with respect to the racket holder in directions parallel to said plane, a clamp carried by the support and movable perpendicularly to said plane and including jaws thereby jointly movable generally into said plane and closable to grip a strung string, means for closing the jaws to grip a string, characterized by: means for locking the support to the turntable; said turntable including a spool having its axis near the center of the racket, fixed to the turntable and having a deep annular groove therein; and said clamp support and means for locking both being bifurcated and straddling the axis and being jointly effective to lock the clamp supPort means by force-spreading against the walls forming the groove.
 16. In a machine for stringing rackets having a turntable, a racket holder thereon for holding a racket in a given plane, a tension-holding assembly including a clamp support movable with respect to the racket holder in directions parallel to said plane, a clamp carried by the support and movable perpendicularly to said plane and including jaws thereby jointly movable generally into said plane and closable to grip a strung string, means for closing the jaws to grip a string, characterized by: means for locking the support to the turntable; said turntable including a spool having its axis near the center of the racket, fixed to the turntable and having a deep annular groove therein; and said clamp support and means for locking both being bifurcated and straddling the axis and being jointly effective to lock the clamp support means by force-spreading against the walls forming the groove; the means for closing the jaw being arranged to perform the force-spreading by reaction to the closing effort.
 17. In a machine for stringing rackets having a turntable, a racket holder thereon for holding a racket in a given plane, a tension-holding assembly including a clamp support movable with respect to the racket holder in directions parallel to said plane, a clamp carried by the support and movable perpendicularly to said plane and including jaws thereby jointly movable generally into said plane and closable to grip a string, characterized by: means for locking the support to the turntable; and string-tensioning means including a pull clamp, means for moving the pull clamp along a line selected at will from a variety of parallel lines displaced laterally with respect to the general direction of pull, and with selected force, and means for locking the turntable during the pull.
 18. In a machine for stringing rackets having a turntable, a racket holder thereon for holding a racket in a given plane, a tension-holding assembly including a clamp support movable with respect to the racket holder in directions parallel to said plane, a clamp carried by the support and movable perpendicularly to said plane and including jaws thereby jointly movable generally into said plane and closable to grip a strung string, means for closing the jaws to grip a string, characterized by: means for locking the support to the turntable; said turntable including a spool having its axis near the center of the racket, fixed to the turntable and having a deep annular groove therein; and said clamp support and means for locking both being bifurcated and straddling the axis and pivotally associated to each other to lock the clamp support by pivotal action causing locking engagement within the groove; said clamp having a toggle linkage which upon being straightened thrusts in one direction to cause pivoting of the levers and in the opposite direction for closing the clamp.
 19. In a machine for stringing rackets, having a racket holder for holding a racket in a given plane, a tension-holding assembly including clamp support means movable with respect to the racket holder in crossing directions parallel to said plane, a clamp movable with the support means and including jaws further movable to grip a strung string, means for closing the jaws to grip a string, and means for locking the support means against all movement along said plane to hold the gripped string, said clamp being pivotal as to its support means about an axis generally perpendicular to said plane for alignment of its jaws with a string strung in either of the crossing directions for gripping said string; said clamp being a toggle clamp in which the jaw closing toggle exerts a thrust perpendicular to the plane to thrust the jaws into adjacency to the strings before gripping the strings and to actuate the means for locking the support. 